Substrates are processed or otherwise exposed to plasma for numerous reasons. Examples include etching material from the substrate, depositing a material on the substrate, or to treat or otherwise modify a material already deposited on the substrate without necessarily etching it therefrom. The invention was principally motivated in plasma processing associated with semiconductor substrates. In the context of this document, the term “semiconductor substrate” or “semiconductive substrate” is defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
Plasma generation and application can occur in a number of manners, for example by RF and microwave means. One particular type of plasma generation includes surface microwave plasma. In the context of this document, “surface microwave plasma” is defined as a plasma generated in a gas against a substrate being processed by transmitting microwave energy from a plurality of discrete, spaced microwave emitting sources, and whether conducted in existing or yet-to-be-developed manners. One existing manner of doing so is by use of an antenna, such as a surface plane antenna (SPA) or a radial line slot antenna (RLSA). By way of example only, examples can be found in U.S. Pat. Nos. 6,399,520 and 6,343,565.
Existing such antennas are typically composed of a material that is blocking of microwave energy (i.e., metal) and which includes an array of microwave transmissive openings formed therethrough. The openings might be completely void of material, or might include solid or other microwave transmissive material, for example silicon dioxide. Appropriate microwave energy applied to the backside of the antenna propagates radially across the antenna and through the individual openings. A gas is flowed between the antenna and the substrate being processed for generating a surface microwave plasma from the gas by the energy applied through the openings. Such can be used to provide a very low power plasma, which is radially equally distributed across a substrate surface being processed and which can be precisely controlled.
The size, shape, and correspondingly, the effective pattern of openings on the surface plane antennas is typically determined by or optimized for the species of gases which are used for the plasma processing. Specifically, different gases (of course, including mixtures of gases) have different ionization potentials in part due to atomic weight and the availability of electrons in outer shells. Accordingly ideally, the size and shape of the openings are optimized depending upon what gas is being utilized. Typically, this means that different antenna designs are utilized for different processing gases, including mixtures of different processing gases. This can undesirably require the changing of the surface plane antennas intermediate processing with different gases, or providing a compromise antenna for certain mixtures of different gases which is not often optimized for any one gas or mixture of gases.
While the invention was motivated in addressing the above-described issues and problems, it is in no way so limited. The invention is only limited by the accompanying claims as literally worded, without interpretative or limiting reference to the specification and drawings, and in accordance with the doctrine of equivalents.